1. Field of the Invention
The application pertains to a method as well as a device for measurement of exposure times in optical devices that have a microscopic imaging path, an observation path, a measuring ray path, and a projection path.
2. Description of the Prior Art
In the measurement of the exposure times in a photomicrographic device, a microscopic chamber or a photometric device, the light of the intermediate image is in most cases split into an observation and a measuring path. Furthermore, only a certain part of the viewing field is used for measurement. The known exposure measurement methods, or devices, respectively, can be divided into three system groups. They are depicted schematically in FIGS. 1-3.
FIG. 1 depicts an imaging path (A) and a measurement path (M) on its extension on which a pre-centered fixed measuring diaphragm (40) is positioned. An observation path (B) is diverted by the reflecting prism (41) with an eyepiece intermediate image plane (19). At location 19 an exactly adjusted graticule is located conjugate to the position of the measuring diaphragm image in the intermediate image. This known principle is used in simple camera attachments for microscopes. The disadvantage consists in the fact that only fixed measuring diaphragms are possible. Moreover, the image of the lines of the graticule (42) is not visible on dark areas of a specimen. Whereas it would be possible with this known projection principle to use several measuring diaphragms, the chosen measuring diaphragm cannot, however, be prominently imaged in the eyepiece.
In FIG. 2 an additional known variant is depicted in which a position and size variable measuring diaphragm (43) is reflected back to the eyepiece intermediate image plane (19) using a light source (L), a hinged mirror (44), a prism system (P) with a semi-transmissive surface (39) and a triple mirror (T). The form and position of a detailed measuring diaphragm is imaged in its temporary condition with this known arrangement. This principle is realized, for instance, in reverse mirror binotubes. The position variable measuring diaphragm of a camera attachment or the size variable measuring diaphragm of a photometer can be backwardly reflected. The greatest disadvantage of this arrangement is that it requires a high degree of optical and mechanical expense and that the occurring stray light part leads to undesirable lightened areas and reflections, because only a maximum of 25% of the light, that is projected back is available. Furthermore it is disadvantageous that the specimen is illuminated by the reverse projection at the diaphragm and can thus only be alternatively indicated or measured.
In the third known projection system, that also shows a measuring diaphragm (40) in the measuring path (M) and a prism system (P) with a semi-transmissive surface (39), the contour of the measuring diaphragm (40) is reflected to the eyepiece intermediate image plane (19) through the projection path (E). The carrier that shows the contours of the measuring diaphragm is positioned in the plane (45) that is conjugate to 19. The arrangement described in FIG. 3 is utilized for the format depiction in available photomicroscopic devices. It would be conceivable in principle to use synchronized continuously adjustable measuring and reflecting diaphragms. However, the movement as well as the form and/or size change of a measuring diaphragm would have to be exactly duplicated by the reflecting diaphragm positioned in the reflecting path (E). This would mean an extremely high mechanical expenditure which could not be realized under presently acceptable cost and manufacturing standards. An additional disadvantage of this third known reflecting principle is that variable measuring diaphragms and their complementary contours are very difficult to realize.